Investigating the relationship between listeria monocytogenes and leaf vegetables and the use of volatile organic compounds for detecting contamination

Bruyniks, Nico 2025. Investigating the relationship between listeria monocytogenes and leaf vegetables and the use of volatile organic compounds for detecting contamination. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Listeria monocytogenes (Lm) is considered a high-risk foodborne pathogen due to its high mortality rate. Lm has predominantly been associated with ready-to-eat (RTE) animal products but is increasingly detected in RTE salads. However, the factors contributing to Lm contamination of salad have not been well investigated. With the growing demand for healthy, nutritious RTE foods and the increasing association of Lm with salads, the risk of foodborne infections rises. Conventional detection methods for Lm in salad take too long to identify contamination within a suitable timeframe. Analysis of volatile organic compounds (VOCs) released from foods has been proposed as a faster alternative to identify bacterial contamination. This study aims to improve understanding of Lm's interaction with salad leaves and develop a VOC-based detection method for Lm to improve food safety. In this study, 15 Lm strains isolated from the produce supply chain, along with 2 reference strains, were examined for genetic and phenotypic characteristics linked to vegetable contamination. NLmo8 and NLmo15 exhibited phenotypic characteristics suggesting a capacity for contaminating leafy vegetables and were examined for their attachment to salad leaves, alongside phylogenetically related strains. Strain-specific differences in attachment were observed. Microscopy and a novel assay were employed to determine whether these differences were due to variations in preferential attachment sites. NLmo8 exhibited the greatest attachment to various plant surfaces. Therefore, NLmo8 was used to determine whether VOC profiles from inoculated rocket leaves could be differentiated from uninoculated leaves. Retail-ready rocket leaves from different years and seasons were sampled, and inoculated leaves could be differentiated from uninoculated ones in 3 of 4 batches. The VOC analysis method demonstrated specificity, as VOC profiles from rocket leaves inoculated with L. innocua could be differentiated from those inoculated with Lm. Analysis of 25 VOCs consistently identified across the 4 batches enhanced the differentiation of Lm-inoculated leaves.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	3 March 2026
Last Modified:	05 Mar 2026 10:34
URI:	https://orca.cardiff.ac.uk/id/eprint/185408

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